1. Technical Field
The present invention relates to a focal plane shutter for a camera including two shutter blades having a plurality of blades.
2. Description of the Related Art
Among focal plane shutters for a camera, a focal plane shutter including two shutter blades referred to as a first blade and a second blade is known and is adopted not only in digital cameras but also in silver salt film cameras. However, this type of focal plane shutter forms two blade chambers by partitioning the space between a shutter base plate and an auxiliary base plate (also referred to as a cover plate or the like) with an intermediate plate (referred to as a partition plate or the like), and two shutter blades are separately arranged in the blade chambers.
Both of the two shutter blades include two arms having one end of each arm individually and pivotally attached to the shutter base plate, and a plurality of blades having one longitudinal end of each blade pivotally supported in order on both the arms toward the free ends of the arms. In the blade chamber, the plurality of blades are arranged closer to the intermediate plate than the two arms. Therefore, both the shutter blades are pivotally supported on a first pivotally attached portion of the two arms, or always come in contact with the intermediate plate. When the shutter blade retreats from the exposure opening, the amount of mutual overlap between the plurality of blades is increased to bring about an overlap state, and when the shutter blade covers the exposure opening, the amount of mutual overlap between the plurality of blades is reduced to bring about the development state.
When the two shutter blades having such a configuration perform an exposure operation, first, a first shutter blade in the development state is made to start an operation so as to open the exposure opening, and then, a second shutter blade in the overlap state is made to start an operation in the same direction so as to cover the exposure opening, and a slit is formed between the slit forming blades to expose an imaging surface. However, it is known that a spring or motor is used as a drive source when performing the exposure operation.
One of them, that is, a case in which a spring is used as the drive source is configured such that a first driving member which links a driving pin to one of the arms of the first shutter blade is rotated by the urging force of a first driving spring, and a second driving member which links a driving pin to one of the arms of the second shutter blade is rotated by the urging force of a second driving spring. However, there are a direct type and a locking type according to a difference in type in which the first driving member and second driving member are held in a state immediately before the start of the exposure operation. JP-A-2008-216484 describes a direct type focal plane shutter having such a configuration, and JP-A-2008-164805 describes a locking type focal plane shutter.
In the case of the focal plane shutter which performs the exposure operation using a spring as the drive source in this way, even in the direct type or even in the locking type, it is known that not only the second shutter blade but also the first shutter blade is brought into the overlap state before photographing so as to fully open the exposure opening and allow the image of a subject to be photographed to be observed with a monitor via an imaging element, and if a release button is pushed when photographing is performed, the first shutter blade is brought into the development state from the overlap state, and then the exposure operation is performed as described above. JP-A-2007-298544 describes a direct type focal plane shutter configured in this way.
On the other hand, as a case where a motor is used as the drive source, it is known that an output pin (driving pin) integral with a rotor of a first motor is linked to one of the arms of the first shutter blade, and an output pin (driving pin) of a rotor of a second motor is linked to one of the arms of the second shutter blade. JP-A-2004-264468 describes a focal plane shutter configured in this way as a second example.
The focal plane shutter of this configuration can operate the first shutter blade to the overlap state from the development state and operate the second shutter blade to the development state from the overlap state whenever photographing is performed in an exposure operation. Besides, the focal plane shutter can operate the second shutter blade to the overlap state from the development state and operate the first shutter blade to the development state from the overlap state, in the next photographing operation, in a case where the first shutter blade is operated to the overlap state from the development state and the second shutter blade is operated to the development state from the overlap state in the previous photographing operation.
The focal plane shutter of this configuration brings not only the second shutter blade but also the first shutter blade into the overlap state before photographing so as to fully open the exposure opening and allow the image of a subject to be photographed to be observed with a monitor via an imaging element, and if a release button is pushed when photographing is performed, any one of the first shutter blade and the second shutter blade is brought into the development state from the overlap state, and then the exposure operation can be performed as described above, or if the release button is pushed when photographing is performed, the first shutter blade and the second shutter blade are alternately brought into the development state from the overlap state whenever photographing is performed, and then the exposure operation can be performed as described above. The present invention relates to a focal plane shutter including two shutter blades which is adapted such that a shutter blade in the overlap state is operated to the development state immediately after the release button is pushed when photographing is performed.